Many electronic systems combine analog and digital technology. In such systems, the analog portion may require a current, voltage or capacitance that is equal to some absolute value. A predetermined, digital value may be used to control a circuit that trims the current, voltage or capacitance.
Existing systems and methods for storing trimming values have used a fuse to generate a logic value. A fuse may comprise polysilicon doped to render it conductive or a metal link. Each fuse may represent a single bit of data. If the fuse is blown, then the fuse may represent a high logic value. If, however, the fuse not blown, the fuse may represent a low logic value. During production of an integrated circuit device, a plurality of fuses may be set to form a predetermined digital value for use in trimming an analog signal. Existing systems and methods use sensing circuits to determine whether each fuse is blown or not blown. However, existing systems and methods exhibit several problems in implementing the fuse technology.
Unlike a discrete fuse, after an integrated circuit fuse has blown, a portion of the fuse may grow back. Effectively, this erases the stored value because sensing circuits in existing systems and method may be unable to distinguish between a fuse that has some grow back and a fuse that has not been blown. Additionally, existing systems and methods do not provide for updating the value of a fuse once it is set in a circuit. Therefore, a new trimming value may not be introduced into a circuit once it has been fabricated.